Sapphire hemispherical domes are machined through milling and shaping using brazed diamond tools.A mathematical model describing roughness for this processing method is established,and the relationship between roughne...Sapphire hemispherical domes are machined through milling and shaping using brazed diamond tools.A mathematical model describing roughness for this processing method is established,and the relationship between roughness and its influencing factors is analyzed.Experiments on the hemispherical dome shaping process are conducted to validate the model,analyzing the variation in roughness under different tool and workpiece rotational speeds.The results are consistent with the predictions of the established roughness model,suggesting that the model can be used to guide subsequent process experiments.Milling and shaping efficiency using brazed diamond tools typically can reach 14 g/min.The machined sapphire surfaces exhibit relatively few microcracks and minimal damage,with almost all exclusively visible grooves resulting from brittle fracture removal.The surface roughness after machining is below 2.5μm.Milling sapphire domes with brazed diamond tools represents a novel shaping technique characterized by high efficiency and high quality.展开更多
High-energy continuous wave(CW)lasers are mostly used in laser damage applications,but efficient laser ablation of transparent materials is challenging due to low optical absorption.Considering the potential of femtos...High-energy continuous wave(CW)lasers are mostly used in laser damage applications,but efficient laser ablation of transparent materials is challenging due to low optical absorption.Considering the potential of femtosecond(fs)laser-induced air filament for high-peak laser transmission over long distances,femtosecond(fs)laser-induced air filaments are combined with a millisecond(ms)laser to form an fs-ms CPL,enhancing the efficiency of sapphire ablation through synchronized spatial-temporal focusing.Experimental results show that ablation efficiency increases with the ms peak power and duty ratio.Excessive thermal stress leads to fragmentation of the sapphire when the ms duty ratio is over 30%at the peak power of 800 W,or when the peak power is over 500 W at a duty ratio of 100%.Also,the mechanism of high-efficiency damage is revealed through in-situ high-speed imaging.According to it,the ablation process went through 4 stages within 1.5 ms:defect-creating,melting and ablation,spattering,and fragmentation.Finally,the equivalent ablation efficiency of the fs-ms CPL is as high as 1.73×10^(7)μm^(3)/J,about 28 times higher compared to the fs laser only.The CPL damage method explored in this paper can provide theoretical guidance for efficient laser damage of transparent materials.展开更多
GHz burst-mode femtosecond(fs)laser,which emits a series of pulse trains with extremely short intervals of several hundred picoseconds,provides distinct characteristics in materials processing as compared with the con...GHz burst-mode femtosecond(fs)laser,which emits a series of pulse trains with extremely short intervals of several hundred picoseconds,provides distinct characteristics in materials processing as compared with the conventional irradiation scheme of fs laser(single-pulse mode).In this paper,we take advantage of the moderate pulse interval of 205 ps(4.88 GHz)in the burst pulse for high-quality and high-efficiency micromachining of single crystalline sapphire by laser induced plasma assisted ablation(LIPAA).Specifically,the preceding pulses in the burst generate plasma by ablation of copper placed behind the sapphire substrate,which interacts with the subsequent pulses to induce ablation at the rear surface of sapphire substrates.As a result,not only the ablation quality but also the ablation efficiency and the fabrication resolution are greatly improved compared to the other schemes including single-pulse mode fs laser direct ablation,single-pulse mode fs-LIPAA,and nanosecond-LIPAA.展开更多
With the growing demand for the fabrication of microminiaturized components,a comprehensive understanding of material removal behavior during ultra-precision cutting has become increasingly significant.Single-crystal ...With the growing demand for the fabrication of microminiaturized components,a comprehensive understanding of material removal behavior during ultra-precision cutting has become increasingly significant.Single-crystal sapphire stands out as a promising material for microelectronic components,ultra-precision lenses,and semiconductor structures owing to its exceptional characteristics,such as high hardness,chemical stability,and optical properties.This paper focuses on understanding the mechanism responsible for generating anisotropic crack morphologies along various cutting orientations on four crystal planes(C-,R-,A-,and M-planes)of sapphire during ultra-precision orthogonal cutting.By employing a scanning electric microscope to examine the machined surfaces,the crack morphologies can be categorized into three distinct types on the basis of their distinctive features:layered,sculptured,and lateral.To understand the mechanism determining crack morphology,visualized parameters related to the plastic deformation and cleavage fracture parameters are utilized.These parameters provide insight into both the likelihood and direction of plastic deformation and fracture system activations.Analysis of the results shows that the formation of crack morphology is predominantly influenced by the directionality of crystallographic fracture system activation and by the interplay between fracture and plastic deformation system activations.展开更多
The finite-element method has been used to study the thermal stress distribution in large-sized sapphire crystals grown with the sapphire growth technique with micro-pulling and shoulder-expanding at cooled center （S...The finite-element method has been used to study the thermal stress distribution in large-sized sapphire crystals grown with the sapphire growth technique with micro-pulling and shoulder-expanding at cooled center （SAPMAC） method. A critical defect model has been established to explain the growth and propagation of cracks during the sapphire growing process. It is demonstrated that the stress field depends on the growth rate, the ambient temperature and the crystallizing direction. High stresses always exist near the growth interfaces, at the shoulder-expanding locations, the tailing locations and the sites where the diameters undergo sharp changes. The maximum stresses always occur at the interface of seeds and crystals. Cracks often form in the critical defect region and spread in the m-planes and a-planes under applied tensile stresses during crystal growth. The experimental results have verified that with the improved system of crystal growth and well-controlled techniques, the large-sized sapphire crystals of high quality can be grown due to absence of cracks.展开更多
MOCVD-grown 0.25μm gate-length AlGaN/GaN high electron mobility transistors （HEMTs） are fabricated on sapphire substrates. A peak extrinsic transconductance of 250mS/mm and a unity current gain cutoff frequency （f...MOCVD-grown 0.25μm gate-length AlGaN/GaN high electron mobility transistors （HEMTs） are fabricated on sapphire substrates. A peak extrinsic transconductance of 250mS/mm and a unity current gain cutoff frequency （fT） of 77GHz are obtained for a 0.25μm gate-length single finger device. These power devices exhibit a maximum drain current density as high as 1.07A/mm. On-chip testing yielded a continuous-wave output power of 27. 04dBm at 8GHz with an associated power-added efficiency of 26. 5% for an 80 × 10μm device.展开更多
A crystalline sapphire （Al2O3） boule （Ф10 × 80mm^3） grown by the temperature gradient technique （TGT） is a bit colored due to carbon volatilization from the graphite heater at high temperatures and the abs...A crystalline sapphire （Al2O3） boule （Ф10 × 80mm^3） grown by the temperature gradient technique （TGT） is a bit colored due to carbon volatilization from the graphite heater at high temperatures and the absorption of transitional metal inclusions in the raw material. The sapphire becomes colorless and transparent after decolorization and decarbonization in successive annealings in air and hydrogen at high temperatures. The quality, optical transmissivity,and homogeneity of the sapphire are remarkably improved.展开更多
Fabrication and characteristics of cascade connected AlGaN/GaN HEMTs grown on sapphire substrates are reported.The circuit employs a common source device,which has a gate length of 0.8μm cascode connected to a 1μm c...Fabrication and characteristics of cascade connected AlGaN/GaN HEMTs grown on sapphire substrates are reported.The circuit employs a common source device,which has a gate length of 0.8μm cascode connected to a 1μm common gate device.The second gate bias will not only remarkably affect saturated current and transconductance,but also realize power gain control.Cascode device exhibits a slight lower of f T,a less feedback,a largely greater of maximum available gain and a higher impedance compare to that of common source device.展开更多
AIGaN/GaN high electron mobility transistors grown on sapphire substrates with a 0.3μm gate length and 100μm gate width are fabricated. The device reveals a drain current saturation density of 0.85A/mm at a gate vol...AIGaN/GaN high electron mobility transistors grown on sapphire substrates with a 0.3μm gate length and 100μm gate width are fabricated. The device reveals a drain current saturation density of 0.85A/mm at a gate voltage of 0V and a peak transconductance of 225mS/mm. The unity current gain cutoff frequency and maximum frequency of oscillation are obtained as 45 and 100GHz,respectively. The output power density and gain are 1.8W/mm and 9.5dB at 4GHz,and 1.12W/mm and 11.5dB at 8GHz.展开更多
Gallium Nitride film was successfully separated from sapphire substrate by laser radiation. The absorption of the 248 nm radiation by the GaN at the interface results in rapid thermal decomposition of interfacial laye...Gallium Nitride film was successfully separated from sapphire substrate by laser radiation. The absorption of the 248 nm radiation by the GaN at the interface results in rapid thermal decomposition of interfacial layer, yielding metallic Ga and N2 gas. The substrate can be easily removed by heating above the Ga melting point (29°C). X-ray diffraction, atomic force microscopy and photoluminescence of GaN before and after lift-off process have been performed, which demonstrated that the separation and transfer process do not alter the structural quality of the GaN films. And further discussions on the threshold energy and crack-free strategies of laser lift-off process have also been presented.展开更多
Monoclinic gallium oxide(Ga_2O_3) has been grown on(0001) sapphire(Al_2O_3) substrate by plasma-assisted molecular beam epitaxy(PA-MBE). The epitaxial relationship has been confirmed to be [010]( 2ˉ01) β-Ga_2O_3||[ ...Monoclinic gallium oxide(Ga_2O_3) has been grown on(0001) sapphire(Al_2O_3) substrate by plasma-assisted molecular beam epitaxy(PA-MBE). The epitaxial relationship has been confirmed to be [010]( 2ˉ01) β-Ga_2O_3||[ 011ˉ0](0001)Al_2O_3 via in-situ reflection high energy electron diffraction(RHEED) monitoring and ex-situ X-ray diffraction(XRD) measurement. Crystalline quality is improved and surface becomes flatter with increasing growth temperature, with a best full width at half maximum(FWHM) of XRD ω-rocking curve of( 2ˉ01) plane and root mean square(RMS) roughness of 0.68° and 2.04 nm for the sample grown at 730 °C,respectively. Room temperature cathodoluminescence measurement shows an emission at ～417 nm, which is most likely originated from recombination of donor–acceptor pair(DAP).展开更多
Single-crystal sapphire is utilized as a high-performance engineering material,especially in extreme and harsh environments.However,due to its extreme hardness and brittleness,the machinability of sapphire is still a ...Single-crystal sapphire is utilized as a high-performance engineering material,especially in extreme and harsh environments.However,due to its extreme hardness and brittleness,the machinability of sapphire is still a challenge.By means of nanoindentation and plunge-cut experiments,the anisotropic brittle-ductile transition of the prismatic M-plane and rhombohedral R-plane is examined by analyzing crack morphologies and the critical depth-of-cut(CDC).The experimental results of the nanoindentation tests are correlated to the plunge-cut experiment.Both the prism plane and the rhombohedral crystal plane exhibit a two-fold symmetry of ductility with various crack patterns along the machined grooves.The direction-dependent plasticity of the hexagonal sapphire crystal is mainly connected to a twinning process accompanied by slip dislocation.展开更多
Non-spherical colloidal silica nanoparticle was prepared by a simple new method, and its particle size distribution and shape morphology were characterized by dynamic light scattering(DLS) and the Focus Ion Beam(FIB) ...Non-spherical colloidal silica nanoparticle was prepared by a simple new method, and its particle size distribution and shape morphology were characterized by dynamic light scattering(DLS) and the Focus Ion Beam(FIB) system. This kind of novel colloidal silica particles can be well used in chemical mechanical polishing(CMP) of sapphire wafer surface. And the polishing test proves that non-spherical colloidal silica slurry shows much higher material removal rate(MRR) with higher coefficient of friction(COF) when compared to traditional large spherical colloidal silica slurry with particle size 80 nm by DLS. Besides, sapphire wafer polished by non-spherical abrasive also has a good surface roughness of 0.460 6 nm. Therefore, non-spherical colloidal silica has shown great potential in the CMP field because of its higher MRR and better surface roughness.展开更多
Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamen...Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.展开更多
The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates （PSSes） with different values of fill factor （f） and slanted angle （0） are investigated in detail. The threading dis...The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates （PSSes） with different values of fill factor （f） and slanted angle （0） are investigated in detail. The threading dislocation （TD） density is lower in the film grown on the PSS with a smaller fill factor, resulting in a higher internal quantum efficiency （IQE）. Also the ability of the LED to withstand the electrostatic discharge （ESD） increases as the fill factor decreases. The illumination output power of the LED is affected by both 0 and f. It is found that the illumination output power of the LED grown on the PSS with a lower production of tan 0 and f is higher than that with a higher production of tan 0 and f.展开更多
Two-inch Ga_2O_3 films with（ˉ201）-orientation are grown on c-sapphire at 850–1050°C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure β-Ga_2O_3 with a smooth surface has a hig...Two-inch Ga_2O_3 films with（ˉ201）-orientation are grown on c-sapphire at 850–1050°C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure β-Ga_2O_3 with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in β-Ga_2O_3 grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 e V.展开更多
The professional modeling software package CrysVUn was employed to study the process of a large sapphire single crystal growth using Kyropoulos method.The influence of gas pressure on thermal field,solid-liquid interf...The professional modeling software package CrysVUn was employed to study the process of a large sapphire single crystal growth using Kyropoulos method.The influence of gas pressure on thermal field,solid-liquid interface shape,gas velocity field and von Mises stress were studied for the first time.It is found that the root of the seed melt when gas pressure equals to one atmosphere or more than one atmosphere,especially during the seeding period,this result is consistent with the experimental observation,and this paper presents three ways to solve this problem.The temperature gradient and stress decreases significantly as the gas pressure increases.The convexity of the solid-liquid interface slightly increases when the gas pressure increases.Numerical analysis was used to optimize the hot zone design.展开更多
The sapphire （Al2O3） single crystal is a kind of excellent infrared transmission window materials. A large-sized sapphire （Ф225 mm×205 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with...The sapphire （Al2O3） single crystal is a kind of excellent infrared transmission window materials. A large-sized sapphire （Ф225 mm×205 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at cooled center）. Several kinds of inclusion in the large sapphire crystal were investigated by means of an optical microscopy （OM）, scanning electron microscopy （SEM） and electron probe microanalysis （EPMA）. The experimental results show that most inclusions are consisted of solid metallic and non-metallic particles as well as gas pores caused by the impurity of alumina as the raw material, the thermal dissociation of aluminum oxide melt and the reaction of the melt to the crucible material （Mo） at high temperatures. It is also found that in different crystal regions the inclusions are of varied sizes, morphology and chemical compositions. Finally, the measures to reduce and eliminate the inclusions are proposed to improve the crystal quality.展开更多
In this paper, large-sized sapphire （Φ230×210 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center）. Dislocation peculiarity in la...In this paper, large-sized sapphire （Φ230×210 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center）. Dislocation peculiarity in large sapphire boule （0001） basal plane was investigated by chemical etchiing, scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6× 10^1-8.0×10^2 cm^2, in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally, the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method.展开更多
InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl ...InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl indium (TMIn) and N 2 were applied as precursors of In and N, respectively. The quality of as-grown InN films were systematically investigated as a function of TMIn fluxes by means of reflection high-energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), and atomic force microscopy (AFM). The results show that the dense and uniform InN films with highly c-axis preferred orientation are successfully achieved on sapphire substrates under optimized TMIn flux of 0.8 ml min 1 . The InN films reported here will provide various opportunities for the development of high efficiency and high-performance semiconductor devices based on InN material.展开更多
基金supported by the Na-tional Natural Science Foundation of China(No.51675457)the Jiangsu Key Laboratory of Precision and Micro-man-ufacturing Technology.
文摘Sapphire hemispherical domes are machined through milling and shaping using brazed diamond tools.A mathematical model describing roughness for this processing method is established,and the relationship between roughness and its influencing factors is analyzed.Experiments on the hemispherical dome shaping process are conducted to validate the model,analyzing the variation in roughness under different tool and workpiece rotational speeds.The results are consistent with the predictions of the established roughness model,suggesting that the model can be used to guide subsequent process experiments.Milling and shaping efficiency using brazed diamond tools typically can reach 14 g/min.The machined sapphire surfaces exhibit relatively few microcracks and minimal damage,with almost all exclusively visible grooves resulting from brittle fracture removal.The surface roughness after machining is below 2.5μm.Milling sapphire domes with brazed diamond tools represents a novel shaping technique characterized by high efficiency and high quality.
基金Project(52105498) supported by the National Natural Science Foundation of ChinaProject(2021RC3074) supported by the Science and Technology Innovation Program of Hunan Province,China+2 种基金Project(2023YFB4605500) supported by the National Key Research and Development Program of ChinaProject(AHL2022KF04) supported by the Advanced Laser Technology Laboratory of Anhui Province,ChinaProject(kq2402089) supported by the Changsha Natural Science Foundation,China。
文摘High-energy continuous wave(CW)lasers are mostly used in laser damage applications,but efficient laser ablation of transparent materials is challenging due to low optical absorption.Considering the potential of femtosecond(fs)laser-induced air filament for high-peak laser transmission over long distances,femtosecond(fs)laser-induced air filaments are combined with a millisecond(ms)laser to form an fs-ms CPL,enhancing the efficiency of sapphire ablation through synchronized spatial-temporal focusing.Experimental results show that ablation efficiency increases with the ms peak power and duty ratio.Excessive thermal stress leads to fragmentation of the sapphire when the ms duty ratio is over 30%at the peak power of 800 W,or when the peak power is over 500 W at a duty ratio of 100%.Also,the mechanism of high-efficiency damage is revealed through in-situ high-speed imaging.According to it,the ablation process went through 4 stages within 1.5 ms:defect-creating,melting and ablation,spattering,and fragmentation.Finally,the equivalent ablation efficiency of the fs-ms CPL is as high as 1.73×10^(7)μm^(3)/J,about 28 times higher compared to the fs laser only.The CPL damage method explored in this paper can provide theoretical guidance for efficient laser damage of transparent materials.
基金supported by MEXT Quantum Leap Flagship Program(MEXT Q-LEAP)Grant Number JPMXS0118067246.
文摘GHz burst-mode femtosecond(fs)laser,which emits a series of pulse trains with extremely short intervals of several hundred picoseconds,provides distinct characteristics in materials processing as compared with the conventional irradiation scheme of fs laser(single-pulse mode).In this paper,we take advantage of the moderate pulse interval of 205 ps(4.88 GHz)in the burst pulse for high-quality and high-efficiency micromachining of single crystalline sapphire by laser induced plasma assisted ablation(LIPAA).Specifically,the preceding pulses in the burst generate plasma by ablation of copper placed behind the sapphire substrate,which interacts with the subsequent pulses to induce ablation at the rear surface of sapphire substrates.As a result,not only the ablation quality but also the ablation efficiency and the fabrication resolution are greatly improved compared to the other schemes including single-pulse mode fs laser direct ablation,single-pulse mode fs-LIPAA,and nanosecond-LIPAA.
基金supported by the National Science Foundation under Grant No.CMMI-1844821supported by the NSF through the University of Wisconsin Materials Research Science Center(Grant No.DMR-1720415).
文摘With the growing demand for the fabrication of microminiaturized components,a comprehensive understanding of material removal behavior during ultra-precision cutting has become increasingly significant.Single-crystal sapphire stands out as a promising material for microelectronic components,ultra-precision lenses,and semiconductor structures owing to its exceptional characteristics,such as high hardness,chemical stability,and optical properties.This paper focuses on understanding the mechanism responsible for generating anisotropic crack morphologies along various cutting orientations on four crystal planes(C-,R-,A-,and M-planes)of sapphire during ultra-precision orthogonal cutting.By employing a scanning electric microscope to examine the machined surfaces,the crack morphologies can be categorized into three distinct types on the basis of their distinctive features:layered,sculptured,and lateral.To understand the mechanism determining crack morphology,visualized parameters related to the plastic deformation and cleavage fracture parameters are utilized.These parameters provide insight into both the likelihood and direction of plastic deformation and fracture system activations.Analysis of the results shows that the formation of crack morphology is predominantly influenced by the directionality of crystallographic fracture system activation and by the interplay between fracture and plastic deformation system activations.
基金National Defence Pre-research Foundation of China (41312040404)
文摘The finite-element method has been used to study the thermal stress distribution in large-sized sapphire crystals grown with the sapphire growth technique with micro-pulling and shoulder-expanding at cooled center （SAPMAC） method. A critical defect model has been established to explain the growth and propagation of cracks during the sapphire growing process. It is demonstrated that the stress field depends on the growth rate, the ambient temperature and the crystallizing direction. High stresses always exist near the growth interfaces, at the shoulder-expanding locations, the tailing locations and the sites where the diameters undergo sharp changes. The maximum stresses always occur at the interface of seeds and crystals. Cracks often form in the critical defect region and spread in the m-planes and a-planes under applied tensile stresses during crystal growth. The experimental results have verified that with the improved system of crystal growth and well-controlled techniques, the large-sized sapphire crystals of high quality can be grown due to absence of cracks.
文摘MOCVD-grown 0.25μm gate-length AlGaN/GaN high electron mobility transistors （HEMTs） are fabricated on sapphire substrates. A peak extrinsic transconductance of 250mS/mm and a unity current gain cutoff frequency （fT） of 77GHz are obtained for a 0.25μm gate-length single finger device. These power devices exhibit a maximum drain current density as high as 1.07A/mm. On-chip testing yielded a continuous-wave output power of 27. 04dBm at 8GHz with an associated power-added efficiency of 26. 5% for an 80 × 10μm device.
文摘A crystalline sapphire （Al2O3） boule （Ф10 × 80mm^3） grown by the temperature gradient technique （TGT） is a bit colored due to carbon volatilization from the graphite heater at high temperatures and the absorption of transitional metal inclusions in the raw material. The sapphire becomes colorless and transparent after decolorization and decarbonization in successive annealings in air and hydrogen at high temperatures. The quality, optical transmissivity,and homogeneity of the sapphire are remarkably improved.
文摘Fabrication and characteristics of cascade connected AlGaN/GaN HEMTs grown on sapphire substrates are reported.The circuit employs a common source device,which has a gate length of 0.8μm cascode connected to a 1μm common gate device.The second gate bias will not only remarkably affect saturated current and transconductance,but also realize power gain control.Cascode device exhibits a slight lower of f T,a less feedback,a largely greater of maximum available gain and a higher impedance compare to that of common source device.
文摘AIGaN/GaN high electron mobility transistors grown on sapphire substrates with a 0.3μm gate length and 100μm gate width are fabricated. The device reveals a drain current saturation density of 0.85A/mm at a gate voltage of 0V and a peak transconductance of 225mS/mm. The unity current gain cutoff frequency and maximum frequency of oscillation are obtained as 45 and 100GHz,respectively. The output power density and gain are 1.8W/mm and 9.5dB at 4GHz,and 1.12W/mm and 11.5dB at 8GHz.
基金supported by Special Funds for Major Stale Basic Research Project G20000683863 Hi-tech Research Project,Distinguished Young Scientist Grant(60025411)+1 种基金National Nature Science Foundation of China(69976014,69636010,69806006,69987001)benefited from using the laser device of the Pulsed Laser Deposition laboratory in Nanjing University.
文摘Gallium Nitride film was successfully separated from sapphire substrate by laser radiation. The absorption of the 248 nm radiation by the GaN at the interface results in rapid thermal decomposition of interfacial layer, yielding metallic Ga and N2 gas. The substrate can be easily removed by heating above the Ga melting point (29°C). X-ray diffraction, atomic force microscopy and photoluminescence of GaN before and after lift-off process have been performed, which demonstrated that the separation and transfer process do not alter the structural quality of the GaN films. And further discussions on the threshold energy and crack-free strategies of laser lift-off process have also been presented.
基金supported by the National Key R&D Program of China(No.2018YFB0406502)the National Natural Science Foundation of China(Nos.61734001,61521004)
文摘Monoclinic gallium oxide(Ga_2O_3) has been grown on(0001) sapphire(Al_2O_3) substrate by plasma-assisted molecular beam epitaxy(PA-MBE). The epitaxial relationship has been confirmed to be [010]( 2ˉ01) β-Ga_2O_3||[ 011ˉ0](0001)Al_2O_3 via in-situ reflection high energy electron diffraction(RHEED) monitoring and ex-situ X-ray diffraction(XRD) measurement. Crystalline quality is improved and surface becomes flatter with increasing growth temperature, with a best full width at half maximum(FWHM) of XRD ω-rocking curve of( 2ˉ01) plane and root mean square(RMS) roughness of 0.68° and 2.04 nm for the sample grown at 730 °C,respectively. Room temperature cathodoluminescence measurement shows an emission at ～417 nm, which is most likely originated from recombination of donor–acceptor pair(DAP).
基金partially supported by JSPS KAKENHI[Grant no.16K14137,2016]
文摘Single-crystal sapphire is utilized as a high-performance engineering material,especially in extreme and harsh environments.However,due to its extreme hardness and brittleness,the machinability of sapphire is still a challenge.By means of nanoindentation and plunge-cut experiments,the anisotropic brittle-ductile transition of the prismatic M-plane and rhombohedral R-plane is examined by analyzing crack morphologies and the critical depth-of-cut(CDC).The experimental results of the nanoindentation tests are correlated to the plunge-cut experiment.Both the prism plane and the rhombohedral crystal plane exhibit a two-fold symmetry of ductility with various crack patterns along the machined grooves.The direction-dependent plasticity of the hexagonal sapphire crystal is mainly connected to a twinning process accompanied by slip dislocation.
基金Funded by the National Major Scientific and Technological Special Project during the Twelfth Five-year Plan Period(No.2009ZX02030-1)the National Natural Science Foundation of China(No.51205387)the Science and Technology Commission of Shanghai(No.11nm0500300),the Science and Technology Commission of Shanghai(No.14XD1425300)
文摘Non-spherical colloidal silica nanoparticle was prepared by a simple new method, and its particle size distribution and shape morphology were characterized by dynamic light scattering(DLS) and the Focus Ion Beam(FIB) system. This kind of novel colloidal silica particles can be well used in chemical mechanical polishing(CMP) of sapphire wafer surface. And the polishing test proves that non-spherical colloidal silica slurry shows much higher material removal rate(MRR) with higher coefficient of friction(COF) when compared to traditional large spherical colloidal silica slurry with particle size 80 nm by DLS. Besides, sapphire wafer polished by non-spherical abrasive also has a good surface roughness of 0.460 6 nm. Therefore, non-spherical colloidal silica has shown great potential in the CMP field because of its higher MRR and better surface roughness.
基金National Natural Science Foundation of China(51575013,51275011)National Key R&D Program of China(2018 YFB1107500)
文摘Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61006084 and 61076119)the Technical Corporation Innovation Foundation of Suzhou Industrial Park,China (Grant No. SG0962)
文摘The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates （PSSes） with different values of fill factor （f） and slanted angle （0） are investigated in detail. The threading dislocation （TD） density is lower in the film grown on the PSS with a smaller fill factor, resulting in a higher internal quantum efficiency （IQE）. Also the ability of the LED to withstand the electrostatic discharge （ESD） increases as the fill factor decreases. The illumination output power of the LED is affected by both 0 and f. It is found that the illumination output power of the LED grown on the PSS with a lower production of tan 0 and f is higher than that with a higher production of tan 0 and f.
基金Supported by the National Key Research and Development Program of China under Grant No 2017YFB0404201the Solid State Lighting and Energy-Saving Electronics Collaborative Innovation Center,PAPDthe State Grid Shandong Electric Power Company
文摘Two-inch Ga_2O_3 films with（ˉ201）-orientation are grown on c-sapphire at 850–1050°C by hydride vapor phase epitaxy. High-resolution x-ray diffraction shows that pure β-Ga_2O_3 with a smooth surface has a higher crystal quality, and the Raman spectra reveal a very small residual strain in β-Ga_2O_3 grown by hydride vapor phase epitaxy compared with bulk single crystal. The optical transmittance is higher than 80% in the visible and near-UV regions, and the optical bandgap energy is calculated to be 4.9 e V.
文摘The professional modeling software package CrysVUn was employed to study the process of a large sapphire single crystal growth using Kyropoulos method.The influence of gas pressure on thermal field,solid-liquid interface shape,gas velocity field and von Mises stress were studied for the first time.It is found that the root of the seed melt when gas pressure equals to one atmosphere or more than one atmosphere,especially during the seeding period,this result is consistent with the experimental observation,and this paper presents three ways to solve this problem.The temperature gradient and stress decreases significantly as the gas pressure increases.The convexity of the solid-liquid interface slightly increases when the gas pressure increases.Numerical analysis was used to optimize the hot zone design.
基金National Defensive Preliminary Research Funds of China (41312040404)
文摘The sapphire （Al2O3） single crystal is a kind of excellent infrared transmission window materials. A large-sized sapphire （Ф225 mm×205 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at cooled center）. Several kinds of inclusion in the large sapphire crystal were investigated by means of an optical microscopy （OM）, scanning electron microscopy （SEM） and electron probe microanalysis （EPMA）. The experimental results show that most inclusions are consisted of solid metallic and non-metallic particles as well as gas pores caused by the impurity of alumina as the raw material, the thermal dissociation of aluminum oxide melt and the reaction of the melt to the crucible material （Mo） at high temperatures. It is also found that in different crystal regions the inclusions are of varied sizes, morphology and chemical compositions. Finally, the measures to reduce and eliminate the inclusions are proposed to improve the crystal quality.
基金the National Defensive Preliminary Research Funds of China (No. 41312040404)
文摘In this paper, large-sized sapphire （Φ230×210 mm, 27.5 kg） was grown by SAPMAC method （sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center）. Dislocation peculiarity in large sapphire boule （0001） basal plane was investigated by chemical etchiing, scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6× 10^1-8.0×10^2 cm^2, in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally, the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method.
基金supported by the National Natural Science Foundation of China (No. 61040058) (No. 60976006)the Fundamental Research Funds for the Central Universities (No.DUT10LK01)the Science and Technology Foundation for Higher Education of Liaoning Province, China and Science and Technology Innovation Project Foundation for Higher Education School (No.707015)
文摘InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl indium (TMIn) and N 2 were applied as precursors of In and N, respectively. The quality of as-grown InN films were systematically investigated as a function of TMIn fluxes by means of reflection high-energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), and atomic force microscopy (AFM). The results show that the dense and uniform InN films with highly c-axis preferred orientation are successfully achieved on sapphire substrates under optimized TMIn flux of 0.8 ml min 1 . The InN films reported here will provide various opportunities for the development of high efficiency and high-performance semiconductor devices based on InN material.
